21 October, 2017

The right fit (Dec 2013)

20 December, 2013

Ian Morris, director of the British Fluid Power Association (BFPA), looks at the important points to bear in mind when sourcing and installing new or replacement hydraulic hose fittings. Hydraulic hoses are used to supply oil under pressure for motion control in a wide variety of high-powered machinery including excavators, cranes, vehicle brake lines, extruder equipment and much more. And, when supplied and fitted to the right specification in order for a particular piece of equipment to carry out specific industrial or mobile tasks, hydraulic hoses have an impressive track record for operational efficiency and reliability. However, due to the wide variety of types of hydraulic hose available for different applications – articulated, coiled, corrugated, reinforced etc. – when sourcing new or replacement hose fittings it is important to bear in mind a number of factors that can ensure the efficient and safe running of the system, as well as mitigate the risk of downtime caused by premature wear or other types of parts failure. First, it is also important not to 'mix and match' different manufactures' fittings in the same hydraulic hose application. Not all suppliers adhere to the same sizes, thread forms or taper angles, even though two different fittings may look more or less the same. Fittings have thread sizes that are often measured using a number of different formats, such as metric, BSP and MPT. Therefore if information regarding the size and thread form etc. isn't written on the fitting, seek the guidance of someone who is capable of using a thread gauge. Whether in terms of rigid piping or flexible hose fittings, if the part has a thread on it the thread has a form and the form must be known before it is installed. Also to be taken into consideration is the importance of tightening a hydraulic fitting to the torsion level specified by the manufacturer or supplier. Properly trained fitters understand that more torque doesn't necessarily mean more oil tightness. Indeed, more torque can start to damage the thread of the fitting, thus risking its reliability and longevity, as well as potentially making it difficult to unscrew. Any male hose fitting and accompanying female port has been designed to be tightened to a particular determined level of torsion, and each manufacturer will be able to inform you of what that accurate specification is. The manufacturer might point out that, for example, this is uptight and a quarter of a turn, or it might specify an actual torque. Also worth bearing in mind is that the correct level of tightness isn't only important in order to avoid thread damage; some hydraulic fittings tighten down against a clamping ring, locking ring, taper or a soft seal, and if you over-tighten the fitting you may distort these rings or seals, which can result in a faster wear or corrosion. Also, bear in mind is that fittings can be made of different materials for use in particular environments. There are two most commonly used types of material. One is carbon steel, cast, forged or fully machined and often with either a zinc- or chrome-type plating. The next most common material used in the manufacture of hydraulic fittings is stainless steel – most commonly 316 in 'open air' or non-corrosive environments, and alternatives such as 318 in more corrosive environments such as in marine or medical installations. So, always consider the most suitable fitting material for your particular application. Additionally, in the same way that it is not recommended to mix and match fittings made by different manufacturers, it is also important not to mix fittings with different material specifications. By using fittings made of different materials on the same hose application sizeable levels of corrosion may occur, which could result in leaks, even though the hose application might seem to work fine in the early stages. The BFPA and its accredited training partners offer Foundation and Skills courses on hose and fittings best practice. Many association members are also members of the BFPA's Hose Accreditation Scheme. If you would like more information about these courses and/or accredited members of the scheme, please contact the BFPA on 01608 647900. More information is also available on the association's website: www.bfpa.co.uk.





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